Cell surface immunoglobulin mu and gamma chains of human lymphoid cells are of higher apparent molecular weight than their secreted counterparts.

Selected human lymphoma-derived and lymphoblastoid cell lines have been characterized and shown to be useful model systems for the expression of either cell surface Ig, or secretory Ig, or both simultaneously. Daudi and Raji cell lines were shown to express surface IgM with no secretion of IgM. The lymphoblastoid cell lines Tay-3 and RPMI 1788 are high-rate secretors of IgM. The lymphoma cell line BJAB synthesizes both cell surface IgM and secretory IgM. In the secreting cells, we have identified an intracellular mu chain with an apparent molecular weight approximately 2000 less than secreted mu chain. In cells synthesizing surface IgM, a surface mu chain has been identified which has an apparent mol. wt. of approximately 2000 more than secreted mu chain. The intracellular mu chain in these cells is indistinguishable in size from the mature surface mu chain; the Daudi cell line is exceptional in that surface deposition of the intracellular mu chain is preceded, or accompanied, by an increase in apparent mol. wt. The lymphoblastoid cell line Bec-11 synthesized both cell surface IgG and secretory IgG. In Bec-11 cells, a surface form of gamma chain, having a higher apparent mol. wt. than secreted gamma chain, has been resolved. There is no detectable difference between L chains associated with any of the different forms of H chain. A biosynthetic relationship between the different forms of H chain is proposed.